1. Field of the Invention
This invention generally relates to an image processing method and device thereof, and especially to an image processing method and device thereof for processing images with running captions.
2. Description of Related Art
A conventional film mode, for example, a common record mode of a movie film, has 24 complete frames per second; therefore, the frame rate is 24 frame/s (or the frequency of the play is 24 Hz). Some other film mode records 30 complete frames per second, or the frequency of the play is 30 Hz. And the conventional broadcasting methods of visual signals, such as cable television and wireless television etc., generally comprise the broadcasting modes of NTSC (National Television System Committee) and PAL (Phase Alternative Line) etc. The broadcasting frequency of the NTSC is 60 Hz which means 60 interlaced frames per second are received at the end-user terminal from the television station. The broadcasting frequency of the PAL is 50 Hz. Wherein, the interlaced frames are, for example, in the odd-number frames, only the scan lines 1,3,5 . . . etc. (so called as the odd-number scan lines) display images. The even-number scan lines do not display any images. In the even-number frames, only the scan lines 2,4,6 . . . etc. (so called the even-number scan lines) display images; the odd-number scan lines do not have images; vice versa.
Therefore, for a film of 30 Hz or 24 Hz film mode, in order to transmit via the NTSC standard at 60 Hz, the processes of 2:2 pull down or 3:2 pull down should be performed before the transmission. FIG. 1 is a drawing schematically showing a view of a conventional frame converting format of a 30 Hz film mode with 2:2 pull down. As shown in FIG. 1, each frame 101,102 to 130 represents a complete image frame with 30 frames per second. Frame 101 is divided into an image frame 101e, which only even-number scan lines appear on the image, and a frame 101o, which only odd-number scan lines appears on the image. Other frames are processed with the same way. Therefore, 60 interlaced frames per second of 101e, 101o, 102e, 102o to 130e and 130o etc. are achieved. Wherein, the frames with suffix “e” represent that only even-number scan lines appear on the images, and the frames with suffix “o” represent that only odd-number scan lines appear on the images (the following uses the same presentations). Thus, the NTSC standard at broadcasting frequency 60 Hz can be accorded.
FIG. 2 is a drawing schematically showing a view of conventional frame converting format of 24 Hz film mode with 3:2 pull down. As shown in FIG. 2, the frames 201, 202, 203 to 224 represent the complete image frames with 24 frames per second. Wherein, the first frame 201 is divided into the interlaced frames 201e and 201o. Further, the second frame 202 is divided into frames 202e, 202o and 202e etc. Furthermore, the third frame 202 is divided into frames 203e and 203o etc. The other frames are processed with the same way. Thus, 60 frames per second of 201e, 201o, 202e, 202o to 224e and 224o etc. are achieved, and the NTSC standard at broadcasting frequency 60 Hz can be accorded.
Besides, an original film at the film mode of 24 Hz, in order to transmit with the PAL standard at 50 Hz, the process of 2:2 pull down should be performed before the transmission. FIG. 3 is a drawing schematically showing a view of the conventional frame converting format of a 24 Hz film mode with 2:2 pull down. As shown in FIG. 3, the frames 301, 302 to 324 represent the complete image frames with 24 frames per second. The first frame 301 is divided into the interlaced frames 301e and 301o. The other frames are processed with the same way. Therefore, frames 301e, 301o, 302e, 302o to 324e and 324o etc. of 48 frames per second are achieved; and with other processes, the PAL standard at broadcasting frequency 50 Hz can be accorded.
Currently, a higher quality playback mode of an image playback device of an end-user terminal, for example, a High Definition TV (HDTV), in order to get better display definition, will first detect whether the received frames are the interlaced frames processed with 2:2 pull down or 3:2 pull down; further, by the Inverse Telecine (IVTC) process, the interlaced frames will be converted into complete frames before they are played back. For example, after receiving the interlaced frames 201e to 224o shown in FIG. 2, the frames 201e and 201o are combined to get the complete frame 201; the frames 202e and 202o are combined to get the complete frame 202; and other frames are processed with the same way. Accordingly, complete frames 201, 201 to 204 of 24 frames per second are achieved. FIG. 4 is a drawing schematically showing a view of a conventional playback mode of a film after the IVTC process performed with 3:2 pull down. Further, according to the mode of FIG. 4, the complete frame 201 as described is played two times to obtain the frames 201p and 201p; the frame 202 is played three times to obtain the frames 202p, 202p and 202p; and other frames are processed with the same way. Finally, 60 frames per second can be played with the playback mode as shown in FIG. 4. Comparing with the playback mode of a conventional TV which 60 interlaced frames per second are played, the frames played with the playback mode as shown in FIG. 4 are smooth without the effects of drop frame, image displacement or image delay.
However, in the conventional broadcasting mode of the visual signal, running captions are frequently added. In general, the running captions are added directly to the interlaced broadcasting frames, for example, added directly to the interlaced frames 101e, 101o, 102e, 102o to 130e and 130o as shown in FIG. 1, or added directly to the interlaced frames as shown in FIG. 2 or FIG. 3. Next, the interlaced frames with the added running captions are transmitted to the end-user terminal.
FIG. 5 is a drawing schematically showing a view of a conventional frame process mode with an interlace mode after adding running captions. As shown in FIG. 5, when the interlaced frames received by an image playback device of an end-user terminal are, for example, the interlaced frames 201e to 224o as shown in FIG. 2 with addition of the running captions 501e, 501o to 530e and 530o, the conventional image playback device will combine the interlaced frames 201e and 201o to a complete frame 551, and combine the interlaced frames 201o and 202e to a complete frame 552, and the other frames are processed with the same way. Accordingly, 60 frames per second frames 551 to 580 can be achieved. It can be noted that the display quality of the running captions achieved by the mode is excellent. However, the definition of the whole frame is deteriorated. For example, the complete frame 552 is composed of the interlaced frames 201o and 202e which are belonged to two different complete frames 201 and 202 as shown in FIG. 2. Consequently, many images with ragged saw tooth are occurred at the intersections of the images in the frame 552. Therefore, a more suitable process method and device for processing the frames with added running captions is imminent and necessary.